The present invention relates to die casting, and more particularly to apparatus permitting air, but not metal, to exit a die casting die.
Die casting is frequently used as a method for forming articles from molten metal and metal alloys. Typically, two or more die parts are provided such that, when brought together, they form one or more cavities which defines the shape of the articles to be cast. Molten metal is introduced into the cavity and allowed to cool or "freeze." If desired, the metal may be squeeze-cast under high pressure, particularly to yield a heat treatable or weldable casting. Following casting, the die parts are opened and the cast articles are removed.
Typically, the molten metal is introduced into the die by means of a shot sleeve. The introduction of metal is referred to as a "pour" or "shot." The die defines a flow way or flow path through the cavities from the shot sleeve to an exit. As the metal is injected into the die, air exits the die through the exit. Particularly in squeeze casting and other high-pressure techniques, the exit must be closed at the end of the pour to prevent metal from passing through the exit.
Two techniques are generally accepted for closing the exit to the passage of metal. The first technique is the "Hodler System," including a valve that closes when the molten metal comes in contact with the valve. Consequently, air is free to exit the vent until the molten metal reaches the valve, at which time the valve closes.
The second technique is the "Turner System," including a mechanical valve that is closed in response to system timing when the metal is expected to arrive at the valve.
Both valves have disadvantages. First, they are relatively complicated and therefore expensive. Second, like any device with moving parts, the valves are less than perfectly reliable. Third, the Turner System is subject to sensor, timing, and control errors.